1. Field of the Invention
The present invention relates to the field of detection apparatus used to screen for the presence of explosives and other chemical entities.
2. Background Information
An effective screening system for threat compounds such as explosives as well as chemical and biological weapons must be able to collect, concentrate, and analyze trace samples quickly and accurately. Many detection technologies (e.g., mass spectrometry, ion mobility spectrometry, optical spectroscopy, etc.) have been developed over the years and trace detectors now exist that can detect a wide range of explosives and chemical weapons, and to a lesser extent biological weapons. Much less attention has been given to collecting and delivering sample to the detectors, yet this is arguably the most challenging part of a screening system since it must adapt to a wide range of applications and screening scenarios. Furthermore, whereas the specificity of a detector is the key to minimizing false positive rates, the collector/concentrator is of vital importance for maximizing detection rates, since if a trace sample is not delivered to the detector, it will result in a non-detect event.
An effective sampling system must have the following operational characteristics: (1) access the volume containing the contamination, (2) dislodge the contamination, particularly for particles that can stick tightly to materials, (3) concentrate collected vapor and particle material, (4) deliver the material to a trace detector in a step that involves vaporization, and (5) minimize cycle time and carryover effects.
An effective collector/concentrator sampling system for explosives and other threats must be able to collect vapor and particles, and if delivering to a trace detector, convert the particles to vapor. Several vapor and particle sampling systems have been developed in the past, however, they are either optimized for one or the other phase, or are not suitable for trace detectors.
U.S. Pat. No. 6,087,183 issued to Zaromb discloses a method to collect vapor and particles on a liquid film. However, a liquid concentrate is not the preferred medium for a trace detector, which is designed to analyze vaporized sample. U.S. Pat. No. 5,914,454 issued to Imbaro et al. discloses a spray of charged droplets to collect vapor, liquid, and particles, but the sample is also concentrated in a liquid. U.S. Pat. No. 5,855,652 issued to Talley discloses a method for collecting particles and microorganisms into a water sample. U.S. Pat. No. 4,092,218 issued to Fine et al. discloses a method for the selective detection of explosives vapors, but does not show that it is capable of collecting particles.
A series of patents issued to Linker et al. disclose methods to collect explosives particles for trace detectors that have some capability to collect vapor as well. U.S. Pat. No. 6,345,545, issued to Linker et al., discloses a two-stage preconcentrator that uses a metal or other electrically conducting screen to capture particles. Some vapors may also stick to the screen, however, the surface chosen for particle collection is not in general optimal for vapor collection. U.S. Pat. No. 6,523,393, issued to Linker et al., discloses a hand-portable embodiment of the metal screen particle concentrator that makes use of a removable screen that is manually placed first in the high volume flow region and second in the detector region.
The above patents disclose means for sample concentration. Another important component to an overall screening system is a sampling probe for collecting vapor and particles, particularly from hard-to-remove locations and surfaces. U.S. Pat. Nos. 6,334,365 and 5,915,268 issued to Linker et al., disclose the use of air-jets to help dislodge particles from the clothing of individuals in a portal device for screening people for explosives. U.S. Pat. No. 6,708,572, issued to Jenkins et al., also discloses the use of air-jets to dislodge particles from individuals in a portal device.
Trace detectors are extensively used in airports and other venues to screen baggage for explosives. The method typically used to remove material from surfaces are swipes of cloth. This method is effective at collecting residue, however, it requires manual operation and therefore may produce unpredictable results in the collection process. Furthermore it is not effective at collecting vapors.